The present invention relates to a sheet feeder of the type which pushes sheets one by one off the top of a stack. The invention particularly concerns a sheet feeder which can be used in an electrophotographic copying machine.
It is known that in such machines the copy sheets may be constituted by sheets of paper treated with zinc oxide or in general, coated with a photoconductive layer which sheets, after being passed through successive copying stages such as charging, exposure, development and fixing, constitute finished copies of the original to be reproduced.
Sheet feeders are known which lend themselves poorly to being employed with this type of copy sheet. An example of such feeders is that in which the sheets are stacked in a pile with the photoconductive surface facing upwardly and a rotating roller is placed in contact and pressed from above against the stack of sheets; the first sheet of the stack is therefore advanced because of the higher friction existing between the sheet and roller than that between sheet and sheet.
This type of feeder has the disadvantage that the roller always presses in the same area of the stack, thus spoiling the subjacent sheets, especially those at the bottom of the stack itself, which are repeatedly subjected to the sliding actions between sheet and sheet which unavoidably occur in the said area.